1. Field of the Invention
The present disclosure generally relates to methods, processes, chemical reactions, or mixed-chemical technologies for the generation of chlorine dioxide. More particularly, the present disclosure relates to a composition and to a method of humidity-controlled generation of chlorine dioxide in polymers, superabsorbent hydrogels, stimuli-responsive hydrogels, smart materials, and polymeric packaging films.
2. Description of Related Art
Chlorine dioxide is a well-known bleaching agent for paper pulp or flour and is also a well-known biocidal or anti-microbial agent for a broad spectrum of microorganisms in decontamination applications for bacterial spores, vegetative pathogens, viruses, phage, and fungi and molds. Millions of pounds of chlorine dioxide are produced for use in these industrial and technological settings. Large-scale methods for chlorine dioxide production employ the reduction of chlorate in concentrated mineral acid solutions of high normality.
As a decontaminant, it has been widely used for its efficacy, material compatibility, and safety for both users and the environment. However, because of the hazards associated with the condensed phase as a high concentration liquid or solution, chlorine dioxide cannot be pre-generated, then shipped or transported in trucks or other vehicles to distant locations. Rather, it must be generated on-site, at point-of-use, and at-will for use in sanitation, disinfection, chemical decontamination, biological decontamination, and other anti-microbial applications.
There are many documented methods for chlorine dioxide generation. For example, Doona et al. (U.S. Pat. Nos. 7,625,533 and 7,883,640) teach chlorine dioxide {ClO2, oxidation state [Cl(IV)]} production by exothermic effector-driven chemical reactions involving oxidizing sodium chlorite ion through the addition of a chemical reductant and a unique chemical effector in water or aqueous solution. In contradistinction to the art of this unique effector chemistry, previous prior art uses chemical oxidants, or acids for acidification to convert chlorite ion {ClO2−, oxidation state [Cl(III)]} to chlorine dioxide. The effector-driven chemical reaction of U.S. Pat. Nos. 7,625,533 and 7,883,640 generates reactive intermediates through reduction that are actually the entities responsible for chemically oxidizing chlorite ion [Cl(III)] to chlorine dioxide [Cl(IV)]. Certain reductants with special chemical properties and reactivities can convert chlorite ion to chlorine dioxide in water or aqueous solution without requiring a chemical effector or significant exothermic heat production. One such reductant, for example, is formamidinesulfinic acid or its conjugate base (abbreviated FSA, U.S. Pat. No. 9,517,934), which is hereby incorporated herein by reference. The chlorine dioxide produced by all of these prior art chemical systems, whether in solution phase or in the gaseous state, can subsequently be used in myriad practical anti-microbial applications for the inactivation of bacterial cells and spores, fungi, molds, mildew, viruses, and bacteriophage, or for chemical decontamination.
As an alternative method of generation, the continuous reduction of sodium chlorate in high acid (supra) can be carried out in homogeneous chemical or electrochemical reactors. Reductants often include methanol, sulfur dioxide, hydrogen peroxide, and chloride ion. These and other standard processes are described in handbooks and encyclopedias of chemical technology; e.g., Vogt et al., “Ullmann's Encyclopedia of Industrial Chemistry.” The chief reductant is methanol (Sundblad et al., U.S. Pat. No. 5,770,171 and Fredette, U.S. Pat. No. 4,473,540). Automation of the reduction process is taught by Swindells et al. (U.S. Pat. No. 4,081,520).
Arguably the most common high volume oxidation technology involves using chlorine as dichlorine gas or as hypochlorite to oxidize chlorite ion to chlorine dioxide. Refinement of the oxidation process incorporates automatic monitoring as taught by Beardwood (U.S. Pat. No. 7,261,821) and Martens et al. (U.S. Pat. No. 7,504,074). Problems with this method of chlorine dioxide production are detailed by Jefferis, III et al. (U.S. Pat. No. 4,908,188). Jefferis, III et al. teaches the extreme corrosivity of dichlorine gas and its hydrolysis products, and the necessity of preventing accidents and ensuring safety. An attempt was made to reduce the inherent danger of dichlorine oxidation by diluting the gas with carbon dioxide (Rosenblatt et al., U.S. Pat. No. 5,234,678).
Producing chlorine dioxide by chlorate ion reduction in high acid and by dichlorine gas oxidation are processes most suited to controlled, less populated industrial settings. They are less well suited for smaller-scale, more populated environments such as kitchens, hospital rooms, rest rooms, class rooms, homes, boats or recreational vehicles, because all of the reactants and reaction byproducts are often considered too dangerous, corrosive and environmentally hazardous to be used in such domestic, consumer-friendly environments. Methods to circumvent these problems for smaller-scale environments have therefore been developed.
One method for avoiding the dangers of dichlorine gas utilizes its hypochlorite ion hydrolysis product (Aalves, European Pat. App. No. EP 2,962,988). This method is complex and necessitates multiple additions of citric acid to initiate reaction, and the addition of sodium bicarbonate to control pH. As taught by Rosenblatt et al. (U.S. Pat. Nos. 4,504,442 and 4,681,739), persulfate can oxidize chlorite ion to chlorine dioxide. However, this reaction is relatively slow. One of skill in the art would also recognize that it is not necessary to use a chemical oxidant, as an electrolysis cell can accomplish the oxidation. Tremblay et al. (U.S. Pat. No. 7,048,842) teach the use of a porous anode to effect the electrochemical oxidation. Unfortunately, this method requires power and is a highly inefficient process. Because of these inherent difficulties, resort has very frequently been made to acidification of sodium chlorite solutions.
Acidification of sodium chlorite solutions at a pH of 2 or below produces chlorine dioxide gas in a reasonably short period of time due to disproportionation of hypochlorous acid. Many researchers have studied the stoichiometry and kinetics of this disproportionation reaction, which is invariant to the identity of the molecules that provide the proton ions to induce a pH below 2. One such study examines all possible intermediates (Horvath et al., J. Phys. Chem. A 2003, 107, 6966-6973); a second, more limited study eliminates hypochlorite ion as an intermediate by scavenging it with dimethyl sulfoxide (Lehtimaa et al. Ind. Eng. Chem. Res. 2008, 47, 5284-5290). When chlorine dioxide is generated in this manner, the need for concentrated acids, including their transportation, storage, and handling, and the need to dispose of acid hazardous waste, makes technologies based on this reaction chemistry unsuited for use in the high-intensity, rapid-mobility environments characteristic of far-forward military deployments.
The main emphasis of early acidification technology was focused on speeding up the reaction. Utilizing pre-mixed reagents such as sodium chlorite and iron(III) chloride adsorbed on solids has been shown to result in very slow chlorine dioxide release upon addition of liquid water (Lovely, U.S. Pat. No. 3,591,515). Eliminating the adsorbent materials allows the reaction to proceed more rapidly, but necessitates segregation of the two reagents prior to mixing with water. Reactive precursors to a desired chemical reaction can be segregated by barriers well known in the chemical and chemical engineering arts, such as valves or membranes. For example, Roozdar (U.S. Pat. No. 5,407,656) teaches dissolution of precursors in solution or in gel form in separate vessels followed by mixing after opening appropriate valves. Dee et al. (U.S. Pat. No. 7,534,398) teaches the sequestration of reactants in packets made of membrane material that dissolves in water, whereupon the reactants are allowed to mix and react.
For the generation of chlorine dioxide, the traditional prior art teaches the reduction of chlorate ion, oxidation of chlorite ion, or the disproportionation of chlorous acid. These methods are superseded in terms of chemical control, reduced hazards, convenience, and safety to users and the environment by the more recent and technologically advanced methods involving transient reactive intermediates (TRI). The earliest TRI methods teach the reduction of chlorite in the presence of an effector to produce fast-acting intermediates which invoke complex reaction chemistry to generate chlorine dioxide and heat (U.S. Pat. Nos. 7,625,533 and 7,883,640, previously cited above). The inherent reaction chemistry of this type of approach has been explained in detail in Doona et al. (U.S. Pat. No. 9,517,934) for a reaction that does not require an effector, namely, the chemical reaction between FSA and chlorite.
In view of the deficiencies of the above prior art, there is a current need for a composition and/or method for generating chlorine dioxide without the use of corrosive acids or buffers to regulate pH. Additionally, any composition and/or method that could controllably produce different amounts of chlorine dioxide from dry, safe, lightweight, transportable reagents or without the addition of energy or need for specialized equipment would provide a significant advantage over the prior art.